My computer had developed a habit of suddenly restarting while playing Civilization. I thought it might be overheating because I hadn't put back on the side panel of the computer, with a fan in it, which might be the main source of incoming air. That didn't fix it and I didn't really think it was overheating anyway, based on the "touch stuff and see if I get burned or zapped" test yielding negative results (in the diagnostic community, negative means positive, which is the least confusing thing we say).

My next suspicion was a bad stick of RAM. So I did the logical thing, switched them into the other pair of slots. That didn't fix it, which confirmed my suspicion.

Finally I resorted to pulling out one of the two 2gb sticks and replacing it with a pair of 512mb sticks from my old computer. This wasn't as big of a loss as it sounds, since Windows only seemed to recognize 3.5gb of the supposed 4gb total, so I only lost 512mb. Maybe there is some performance impact from having the unpaired stick, but I've not noticed. It is certainly offset by the reliability gain.